Process of producing all skin rayon



United States Patent 3,009,763 PROCESS OF PRODUCING ALL SKIN RAYON John A. Howsmon, Wilmington, Del., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware No Drawing. Filed Apr. 8, 1958, Ser. No. 727,054 Claims. (CI. 18-54) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filamen-t may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying;being collected either before or after these treatments.

The filaments as formed by the conventional methods, consist of a skin or outer shell portion and a large core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stiif.

It has now been discovered that the presence of small amounts of alkali-soluble alkylene oxide adducts of cresol in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like having an exceptionally high percent of skin, and that under certain specific processing conditions produce a product composed of substantially all skin. Products having improved properties and characteristics are obtained providing the amount of the adduct is maintained within certain limits and the composition of the spinning bath is maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as comparedt to conventional filaments include a smooth, non-crenulated surface and the filaments consist of at least 85% skin and in many instances -substantially entirely of skin.

This invention contemplates the use of such compounds as are more technically classed as polyoxyalkylene glycol ethers of cresol such as, for example, the ethers of ethylene and propylene glycols and cresol. 'Ihe adducts or ethers may be derived from the o-, mor p-forms of cresol or from the commercial grades of cresol which consist of a mixture of all three forms or from commercial cresylic acid which is the high cresol-containing fractions distilled from coal tar. The adducts may consist of a mixture of ethers having polyalkylene oxide chains of different length or having polyalkylene oxide chains of substantially the same length. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and in alkali solutions such as a 6% caustic solution, the polyoxyethylene glycol ethers or ethylene oxide adducts of cresol are preferred. Accordingly, the invention will be illustrated specifically by reference to the polyoxyethylene glycol ethers of cresol.

The polyoxyalkylene content of the adducts or ethers should contain an average of at least 4 alkylene oxides such as ethylene oxide units per molecule of cresol, and may be as high as 50 to 100 units, however, there appears to be a tendency of unstability with the higher number of alkylene oxide units. The preferred ethers contain from about 6 to about 25 ethylene oxide units per molecule of cresol. The production of the high percentage and particularly the all skin products requires that certain minimum amounts of the ether be in solution in the viscose. It is obvious, therefore, that the ether must have a sufiicient solubility whereby the minimum amount can be dissolved in the viscose, that is, the ether must be alkalisoluble to at least this extent. The adducts or ethers may be conveniently added to the viscose in the form of a solution in water or in a caustic soda solution.

The amount of the adduct which is incorporated in the viscose must be at least about 0.25% by weight of the cellulose in the viscose and may vary up to about 3.5% to 4%, preferably, the amount varies from 0.5% to 2%. Lesser amounts do not result in the production of products consisting of at least skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The adduct may be added at any desired stage in the production of the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 4% to about 9% cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 11% and the carbon disulfide content may be from about 30% to about 60% based upon the weight of the cellulose. 'Ihe modified viscose, that is, a viscose containing a small amount of the ether or adduct, should have a sodium chloride salt test number above about 7 and preberably about 9 or higher at the time of spinning or extrusion. The salt testis an indication of both the amount of carbon disulfide added to the viscose and the degree of aging. The salt test number is the minimum percent concentration of sodium chloride solution at 18 (3. required to coagulate 3 drops of viscose. It is determined by dropping the viscose in-to a beaker containing about 40 cc. of sodium chloride solution at 18 C. while stirring. Stirring is continued for 90 seconds after the last drop of viscose has been added.

In order to obtain the improvements heretofore mentioned, and particularly to obtain all skin, or substantially all skin yarn with its resulting advantages, it has been found that in addition to the ether modifier in the viscose, the amount of carbon disulfide used in the preparation of the viscose and the concentration of acid and of zinc salts in the spinning bath are important. The presence of the modifier of this invention in a viscose of required carbon disulfide content combined with these spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistance, high fatigue resistance and consisting of filaments composed substantially or entirely of skin.

In practicing the present invention, the carbon disulfide added in preparing the viscose should be at least 32%, based on the bone dry cellulose content, and preferably of the order of 35% to 50%.

Also, generically and in terms of the industrial art, the spinning bath used in the practice of the present invention is a low acid-high zinc spinning bath. The bath should contain from about 10% to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15% to 22% sodium sulfate and from 5% to 12% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 C., though at the lower temperatures the higher concentrations of sodium sulfate cannot be used because of the difiiculty of solubility. However, at the preferred temperatures of between about 45 C. and about 70 C. solubility is no problem. In the production of the all skin type filaments, the temperature of the spinning bath is not critical. However, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength are affected by the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as obtain the desired high tensile strength.

The acidcontent of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. Though for any given spinning conditions, a substantially higher percentage of skin will be obtained through the use of the modifiers of the present invention, in order to obtain an all skin yarn, the carbon disulfide content of the viscose should preferably be at least 35% based on the dry cellulose. Also, the acid content of the spinning bath should preferably not exceed about 9% while the zinc sulfate should preferably be within the range of about 5% to 12%. However, frequently in commercial spinning practice, it is desirable to have a somewhat higher acid content in the spinning bath. It has been discovered that high acid concentrations can be used for any given amount of modifier and still exceptionally high skin and all skin yarns obtained if the carbon disulfide content of the viscose is increased and if the zinc sulfate content of the bath is maintained at a reasonably'hi-gh level such as above 8.0%. Thus, although in practicing the present invention for the production of all skin products it is generally preferred that the acid concentration of the bath not exceed about 9%, all skin products will be obtained at higher acid concentrations up to as high as 11% to 12% if the carbon disulfide content of the viscose is sufficiently increased and the zinc sulfate of the spinning bath is not appreciably below 8.0%. Of course, increasing the amount of modifier, within the range specified,'also permits, to some degree, the use of higher acid it can be stated, in practicing the present invention with I the modifiers mentioned, that if difliculty is encountered in obtaining a 100% skin product because of the desire to use a spinning bath having an acid content in excess of 9%, the difficulty may be overcome by using a viscose of higher carbon disulfide content and by increasing the zinc sulfate content of the bath within the limits indicated.

Though various terminology may be used to indicate the point at which the viscose is sufiiciently coagulated to permit uniform withdrawal from the spinneret, for purposes of the present application, the term slubbing point will be used. This lower acid concentration is readily determined by those skilled in the art through observance of the fibers as formed and has no particular effect on the production of high skin or all skin products in practicing the present invention. In general, the lower limit of sulfuric acid required in order to give sufficient coagulation for spinning, for example, with a viscose containing 7% cellulose and 6% caustic, is about 6%. Another way of stating this is that an acid concentration of about 6% is slightly above the slubbing point. It is apparent that for viscose with higher caustic content, a slightly higher acid concentration would be required due to the partial neutralizing effect of the increased caustic.

It is clear from the above that there is a maximum acid concentration for any specific viscose composition of given carbon disulfide content beyond which substantially all skin products will not be obtained with the present additives. It is also clear that this maximum acid concentration can be somewhat increased through the use of higher concentrations of zinc sulfate in the spinning bath and by increasing the carbon disulfide content of the viscose. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of all and substantially all skin products from an 8% cellulose, 7.5% caustic, 35% carbon disulfide viscose containing the above-mentioned ethers of cresol, lies between about 6.5% and about 8.7%. The acid concentration may be increased as the amount of additive is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of modifier and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid content of the bath is increased above the maximum value although the amount of added modifier is increased to as much as 4% while other conditions are maintained constant. For example, a viscose containing about 8% cellulose, about 7.5 caustic soda, about 35% carbon disulfide based on the dry cellulose and 1% of a polyoxyethylene glycol ether of cresol containing about 8 ethylene oxide units per molecule and having a salt test of about 9 when extruded into spinning baths containing 16% to 20% sodium sulfate, 4% to 8% zinc sulfate and sulfuric acid of not more than about 8.6%, results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amounts of acid result in the production of products having skin and core. At acid concentrations in excess of about 9.5%, the skin generally comprises less than of the filament. By increasing the carbon disulfide content to 45%, however, and increasing the zinc carbon disulfide of the viscose as based on the dry cellulose and is preferably maintained between about 0.20 and 0.22 times the carbon disulfide content of the viscose. It is also generally preferred that the acid content of the spinning bath not exceed about 1.35 times the caustic soda content of the viscose.

The presence of the alkylene oxide adducts of cresol in the viscose retards the regeneration and, therefore the amount of modifier employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning speed of about 50 meters per minute,

follow by reference to the preparation of regenerated cellulose filaments from a viscose modified with an ethylene the modifier is employed in amounts within the lower por tion of the range, for example, about 0.75%. The determination of the specific maximum and optimum concen-- tration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period suflicient to effect relatively complete coagulation of the viscose, that is, the coagulation must be sufficient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 120%, preferably between 80% and 100%. Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step ,a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of alkylene oxide adducts of cresol and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing alkylene oxide adducts of cresol have superior abrasion and fatigue resistance characteristics and have a high flex-life. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic-tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention is illustrated in the examples which oxide adduct of cresol (commercial mixture of o-, mand p-cresol) containing an average of about 8 ethylene oxide units per molecule of cresol, the viscose containing about 8% cellulose, about 7.5% caustic soda, and having a total carbon disulfide content of about 35% based on the weight of the cellulose. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 35% carbon disulfide based on the weight of the cellulose and churning for about 2% hours. The cellulose xanthate was then dissolved in caustic soda solution. The desired amount of the ethylene oxide adduct of cresol was added to the solution and mixed for about /2 hour. In the examples, the proportions of the cresol derivatives are expressed as the percentage by weight of the cellu lose in the viscose. The viscose was then allowed to ripen or about 30 hours at 18 C.

Example 1 Approximately 0.5% (based on the weight of the cellulose) of the ethylene oxide adduct of cresol was added to and incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 14.5 and was extruded through a spinneret to form a 200 denier, 120 filament yarn at a rate of about 22 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 8.7% sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The yarn was stretched about 82% while passing through a hot water bath at C. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. l500 The filaments of a control yarn spun with the same viscose but without the addition of the modifying agent and spun under the same conditions, exhibit a very irregular and serrated surface and are composed of about 70% to 75% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 2 To a viscose as described above, there was added 0.5% of the ethylene oxide adduct of cresol. Theviscose had a salt test of 13 and was spun into a 200 denier, filament yarn by extrusion into a spinning bath containing 8.2% sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were subsequently passed through a hot water bath at 95 C. and stretched about 82%. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The indiw'dual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 70% to 75% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 3 To a viscose solution as described above, there was added 0.5% of the ethylene oxide adduct of cresol. The viscose had a salt test of 9.3 and was spun into a 200 denier, 120 filament yarn by extrusion into a bath containing 8.5% sulfuric acid, 8% zinc sulfate and 17% sodium sulfate. The bath was maintained at a temperature of 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at about 95 C. and the filaments were stretched approximately 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 70% to 75% skin and the balance core with a sharp line of demarkation between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 4 To a viscose solution, prepared as described above, there was added 1% of the ethylene oxide adduct of cresol. The viscose had a salt test of 13.6 and was spun into a 200 denier, 120 filament yarn by extrusion into a bath containing 8.4% sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The bath was maintained at a temperature of about 60 C. The extrusion rate was about 22 meters per minute. The water bath was main tained at a temperature of about 95 C. and the filaments were stretched 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist entirely of skin. Control filaments have a very irregular and serrated surface and consist of about 70% to 75% skin and the balance core with a sharp line of demarkation between the skin and the core. Other characteristics are set forth in the table which follows the examples.

The following example illustrates the effect of the lower zinc content of the spinning bath and spinning of the modified viscose at a lower salt test.

Example To a viscose solution, prepared as described above, there was added 1% of the ethylene oxide adduct of cresol. The viscose had a salt test of 9.8 and was spun into a 200 denier, 120 filament yarn by extrusion into a bath containing 8.5% sulfuric acid, 5.3% zinc sulfate and 20% sodium sulfate. The bath was maintained at a temperature of about 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at a temperature of about 95 C. and the filaments were stretched 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments were readily distinguishable from control filaments prepared from viscose containing no modifier in that they have a smooth, non-crenulated surface and consist of at least 95% skin. Control filaments have a very irregular and serrated surface and consist of about 70% to 75% skin and balance core with a sharp line of demarkation between the skin and the core. Other characteristics are set forth in the table which follows:

Tenacity, grams Elongation, per denier percent Skin,

percent Wet Dry Wet Dry Example 1 Example 2.

NNNNNP mane-anew Hemeecroc the ease and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surfaced, all skin structure and p sess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore. Although the filaments of Example 5 did not consist entirely of skin, they have somewhat greater physical strengths and also have smooth surfaces.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appre ciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The alkylene oxide adducts of cresol may be added to any desired viscose such as those normally used in indus try, the specific viscose composition set forth above, being merely for illustrative purposes. The modifying agent may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the cresol derivatives at the time of spinning.

If desired, small amounts of the modifying agent may be added to the spinning bath. Since the modifying agents are water-soluble to some extent, some of the modifier will be leached from the filaments and will be present in the bath.

The term creso is used herein and in the claims in a generic sense to include the pure forms of cresol, the commercial grades of cresol containing a mixture of the three isomers and such commercial grades as the coal tar fractions which are predominantly a mixture of the three isomers and are in some instances termed cresylic acid.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Myers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestufis Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of -10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

This application is a continuation-in-part of my copend- .ing application Serial No. 519,000, filed June 29, 1955.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a method of producing shaped bodies of regenerated cellulose having an enhanced percentage of skin, the step which comprises extruding viscose containing at least 30% carbon disulfide, based on the weight of the cellulose in the viscose, and containing from about 0.25% to 4%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalkylene glycol ether of cresol containing at least 4 alkylene oxide units per molecule of cresol, into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the percentage sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 0.25 times the percent carbon disulfide based on the cellulose in the viscose.

2. The step in the method as defined in claim 1 wherein the polyoxyalkylene glycol ether is a polyoxyethylene glycol ether of cresol containing from 6 to 26 ethylene oxide units per molecule of cresol.

3. In a method of producing shaped bodies of regenerated cellulose having an enhanced percentage of skin, the steps which comprise adding to and incorporating in viscose containing at least 30% carbon disulfide, based on the weight of the cellulose in the viscose, from about 0.25% to 4%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalkylene glycol ether of cresol containing at least 4 alkylene oxide units per molecule of cresol, ripening the viscose to a sodium chloride salt test of not lower than about 7 and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 10.5%.

4. The steps in the method as defined in claim 3 wherein the polyoxyalkylene glycol ether is a polyoxyethylene glycol ether of cresol containing from 6 to 25 ethylene oxide units per molecule of cresol.

'5. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 0.25% to 4%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalkylene glycol ether of cresol containing at least 4 alkylene oxide units per molecule of cresol into an aqueous spinning bath containing from about 10%' to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%.

6. The step in the method as defined in claim 5 wherein the polyoxyalkylene glycol ether is a polyoxyethylene glycol ether of cresol containing from 6 to 25 ethylene oxide units per molecule of cresol.

7. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the steps which comprise adding to and incorporating in 10 viscose containing at least 30% carbon disulfide, based on the weight of the cellulose in the viscose, from about 0.5% to 2%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalkylene glycol ether of cresol containing at least 4 alkylene oxide units per molecule of cresol and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15 zinc sulfate, and sulfuric acid, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 9%.

8. The steps in the method as defined in claim 7 wherein the polyoxyalkylene glycol ether is a polyoxyethylene glycol ether of cresol containing from 6 to 25 ethylene oxide units per molecule of cresol.

9. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in viscose containing about 8% cellulose, about 7.5% caustic soda and about 35% carbon disulfide, based upon the weight of the cellulose, from about 0.5% to 2%, based on the weight of the cellulose in the viscose, of an alkali-soluble polyoxyalk-ylene glycol ether of cresol containing at least 4 alkylene oxide units per molecule of cresol, ripening the viscose to asa lt point of not lower than about 9 and extruding the viscose into an aqueous spinning bath containing from about 16% to 20% sodium sulfate, from about 4% to 9% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%.

10. The method as defined in claim 9 wherein the polyoxyalkylene glycol ether is a polyoxyethylene glycol ether of cresol containing from 6 to 25 ethylene oxide units per molecule of cresol.

References Cited in the file of this patent UNITED STATES PATENTS 2,535,044 Cox Dec. 29, 1950 2,710,861 Charles et a1. June 14, 1955 2,792,313 Charles et a1. May 14, 1957 2,805,169 Mitchell Sept. 3, 1957 2,841,462 Lytton July 1, 1958 2,852,333 Cox Sept. 16, 1958 2,852,334 Hollihan Sept. 16, 1958 2,895,788 Howsmon July 21, 1959 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE HAVING AN ENHANCED PERCENTAGE OF SKIN, THE STEP WHICH COMPRISES EXTRUDING VISCOSE CONTAINING AT LEAST 30% CARBON DISULFIDE, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, AND CONTAINING FROM ABOUT 0.25% TO ABOUT 4%, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF AN ALKALI-SOLUBLE POLYOXYALKYLENE GLYCOL ETHER OF CRESOL CONTAINING AT LEAST 4 ALKYLENE OXIDE UNITS PER MOLECULE OF CRESOL, INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO ABOUT 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE PERCENTAGE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 0.25 TIMES THE PERCENT CARBON DISULFIDE BASED ON THE CELLULOSE IN THE VISCOSE. 